1. Field of the Invention
The invention relates to an internal combustion engine exhaust gas control system applied to a hybrid vehicle that runs using two types of power sources, one being an internal combustion engine and the other being an electric motor. The invention also relates to a method of controlling such an internal combustion engine exhaust gas control system.
2. Description of the Related Art
In an internal combustion engine exhaust gas control system applied to a hybrid vehicle that runs using two types of power sources, one being an internal combustion engine and the other being an electric motor, the exhaust gas purifying effect is reduced if the catalyst temperature of an exhaust gas control catalyst is below the catalyst activation temperature. In particular, during a cold start of the internal combustion engine, the exhaust gas control catalyst must be warmed up so that it may be activated quickly.
Japanese Patent Application Publication No. 2000-297669 (JP-A-2000-297669) describes technology for quickly activating an exhaust gas control catalyst by increasing the engine load to raise the exhaust gas temperature when the exhaust gas control catalyst is not yet activated, in an internal combustion engine exhaust gas control system which is applied to a hybrid vehicle. Technology which controls the engine to output constant torque and applies a load to the engine by controlling a motor/generator (M/G) to generate power is also described.
However, although increasing the output of the internal combustion engine hastens activation of the exhaust gas control catalyst, it may also cause emission of large amounts of pollutants (e.g., unburned fuel) into the atmosphere until the exhaust gas control catalyst becomes activated. Also, the engine is stopped when the battery is fully charged so it is possible that the internal combustion engine may start up when the exhaust gas control catalyst is not activated, such as during sudden acceleration.